The invention pertains to electric arc furnaces, and particularly pertains to a method and apparatus for readily removing deteriorated refractory lining from the furnace shell and hearth.
Direct arc electric furnaces include a base defining a hearth from which extends an annular wall or shell. The top of the furnace is closed by a removable cover through which the electrodes extend and the cover is removed from the shell during charging of the furnace. The hearth, shell and cover are internally protected from the molten metal by refractory lining material, and the furnace base is tiltable with respect to the horizontal whereby the molten metal therein may be poured from a pouring spout.
In a direct arc electric furnace it is necessary to periodically replace the refractory lining due to the destructive effect upon the lining by the arc and molten metal during furnace operation. The heat, molten metal, oxidation, and many other factors cause the refractory lining to be consumed and the lining must be periodically replaced. In particular, in a continuously operated furnace the shell lining wears especially rapidly and it is often necessary to replace the shell lining every four or five weeks. The hearth lining deteriorates much slower than the shell lining and may require replacement approximately once a year, while the lining in the cover may also be used for extended periods of time before requiring replacement.
With present direct arc electric furnace constructions the replacement of the refractory lining material, particularly the shell lining, is time consuming and expensive. The furnace must be emptied of molten metal, allowed to cool sufficiently to permit entry by the workmen, and the workmen manually, and with power tools, break away the refractory lining for removal from the furnace. After the lining has been removed rebuilding of the lining takes place within the furnace in order to resume operation. The requirement for the cooling of the furnace, and the fact that the workmen must enter the cooled furnace to remove the lining, is both time consuming, dirty and hazardous, yet an improved manner for replacing furnace lining has, heretofore, not been provided.
The use of pivot pins to support the base of electric furnaces is well known as shown in U.S. Pat. Nos. 2,355,095 and 2,472,954. Likewise, the pivotal mounting of electric furnace bases on arcuate segments, either smooth or geared, is known as typically illustrated in U.S. Pat. Nos. 1,304,350 and 3,684,261. Further, the removal of portions of an electric arc furnace, such as the shell, is known as shown in U.S. Pat. Nos. 1,445,860 and 3,723,631. With respect to the removal of the shell, in U.S. Pat. No. 1,445,860 the shell casing and the refractory lining are removed as a unit, while in U.S. Pat. No. 3,723,631 the shell is removed and the furnace construction permits the substitution of one refractory skull for another. However, the aforementioned prior art patents do not present solutions to the problem of replacing the refractory lining of arc furnaces in a practical manner achievable with available equipment and the time consuming expense of periodically replacing furnace refractory lining, particularly shell lining, continues to add significantly to the cost of producing steel by known direct arc electric furnace apparatus.
In. U.S. Pat. No. 1,445,860 replacement of the shell refractory lining is achieved in its entirety whereby one entire shell may be substituted for a deteriorated lining and shell. While such an arrangement would provide short furnace down time and rapid shell refractory lining replacement, difficulty in maintaining the refractory lining in proper relationship during handling, and storage limitations, as well as weakness at the joint lines produced between the hearth and shell lining have prevented the apparatus disclosed in this patent from being acceptable and practical.
The removal of refractory lining from the hearth of an electric furnace is particularly difficult in that such lining is not removed as often as the shell lining, and the lining often consists of a homogeneous material which has hardened requiring the use of pneumatic hammers and other power equipment to break the hearth lining to permit removal by manually "digging out" the lining.